Q. "One of my coworkers told me that you burn more calories during winter because your body needs to work harder to keep your core temperature up. Of course, she was making this argument while eating a piece of cake! But it makes a certain amount of sense. I know that I feel hungrier in winter than summer. Do calorie requirements change when the weather changes?"

A. Your coworker is right: The ambient temperature does affect how many calories you burn to maintain your body temperature. If you spend a lot of time outdoors in cold weather (or you're very thrifty with your home heating), you will burn more calories than you would in a warm room. Research has demonstrated, for example, that decreasing the temperature of a room by 100 F, from a comfortable 720 F (200 C) to a chilly 610 F (160 C), causes people to burn about 150 extra calories per day.

But as you've also noticed, colder temperatures can also stimulate your appetite. In fact, the subjects in the study I just mentioned ate an extra 250 calories a day when the room was cool, more than compensating for the additional calories they burned. This—along with decreased opportunities for exercise--may explain why many people gain weight over the winter, despite the fact that cold temperatures increase calorie expenditure.

An increase in appetite during the winter may be, in part, your body's attempt to make up for the extra calories it's burning to keep you warm. But if (as seems to be the case with your coworker) you find yourself craving sweets and carbs, there may be something else going on as well.

Cooler temperatures are usually accompanied by decreased sunlight, which can affect the production of neurotransmitters. In particular, levels of serotonin (which is sometimes called the "happiness hormone") dip during the winter. Those carb cravings may actually be your body's attempt to raise your serotonin levels--and your mood. Here's a healthier option: Shorter days have you craving carbs? Try this instead.